In liquid processing system, such as boilers and their associated fuel burners, it is substantially essential that the level of the water in the system be verified prior to the initiation or lighting of the fuel burner. The failure to have water present in a boiler at the time the fuel burner is ignited obviously creates an unsafe condition that can either damage the boiler, or possibly even cause an explosion with more extensive damage and possible loss of life.
While the present description is particularly directed to boilers and their associated burners, the problem of verifying the level of a liquid before initiation of processing of the liquid is becoming more and more important due to automation and the safety requirements involved. Boilers generally use water level sensing devices which rely upon float operated switches, resistance type probes, and similar equipment which can fail indicating the presence of water when none is present. Since much of the present equipment is now operating through automated process controls and fuel burner controls, more and more electronic components and circuitry are also being used. This type of circuitry is also subject to unsafe types of failures. A relatively simple means of verifying the liquid level or system circuitry prior to the initiation of the process or burner in a boiler is, therefore, becoming more and more necessary.